In one known method (PCT International Patent Publication No. WO 2006/095515), for better utilization of the fuel and for reducing the nitrogen-oxide emissions, the two fuel injectors are controlled in such a way that when the internal combustion engine is operating in a specific operating range and the control mechanism for the intake valves reduces the opening lift or the opening duration of the intake valves, the portion of the fuel that is injected directly into the combustion engine rises according to the amount of the reduction of the opening lift or the opening duration. The increased direct injection prevents a deterioration of the satisfactory mixing of the fuel in the combustion chamber that is required in a lean mixture combustion.
The increasing use of regenerative fuels such as ethanol requires a bi-fuel utilization by Otto engines, of regular fuel and regenerative fuel and also any mixtures of both types of fuel, without manual resetting being necessary. The low fuel value of ethanol, for instance, calls for the injection of a considerably higher fuel quantity in ethanol operation, and the higher evaporation temperature of ethanol in comparison with gasoline requires yet a further increase in the fuel quantity at very cold temperatures. In internal combustion engines having direct injection, the maximally possible injection quantity is defined by the applied fuel pressure, the throughput of the fuel injectors, and the cycle time specified by the engine speed. Since the throughput of the fuel injectors must be adapted to the minimally required injection quantity for a warm internal combustion engine, only the delivery rate of the fuel pump could be increased to provide the increased fuel quantity.